1. Field of the Invention
The present invention relates to a digital switching equipment, and more particularly, to a digital switching equipment provided with an extra PCM (Pulse Coded Modulation) highway connecting between a card shelf, which mounts electronic circuit cards of a line or trunk interface such as a line circuits card or a trunk circuits card, and a time division switch.
2. Description of the Related Art
The speech path subsystem of the digital switching equipment is constituted by a line circuit or a trunk circuit, which is an interface circuit with a subscriber terminal connected by a subscriber line or an interface circuit with other switching equipment connected by a transmission line, and the time division switch which exchanges voice or data in a time slot between an input time slots stream and an output time slots stream in accordance with necessary routing control performed by a central control unit of the digital switching equipment. The PCM highway is a junction line connecting the line circuit or the trunk circuit with the time division switch, and carries time slots stream between line circuit or trunk circuit and the time division switch.
FIG. 4 is a conceptual drawing showing physical connection arrangement of the speech path subsystem of the digital switching equipment. A card 101, 10N, 201 or 20N is the line circuits or the trunk circuits, and a plurality of such cards are mounted in a shelf 10 or 20 which is provided with a plurality of slots for insertion of cards. Voice or data of a group of cards in one shelf is transferred to the time division switch by one PCM highway HW1 or HW5, and the time slot allocation in the PCM highway is predetermined in accordance with the mounting position of card (or slot number of the shelf). It means that the PCM highway number is corresponding to the shelf and the time slot number in a PCM highway is corresponding to the mounting position of the line circuit or the trunk circuit in a shelf. Usually, one card consists of the plural number of line circuits or trunk circuits.
FIGS. 5(a) to (c) are also conceptual drawings showing examples of correspondence between the time slot number in the PCM highway and mounting position in the shelf.
FIG. 5(a) shows an example that one card consists of three circuits of line circuit or trunk circuit, ten cards are mounted on a shelf, and the PCM highway has 30 time slots of communication channel (time slot number 0 and 16 are used for control signal and not used for communication channel). Correspondence between time slot number of the PCM highway and mounting position of card is predetermined as shown in FIG. 5(a), i.e., the time slot number 1, 2 and 3 of the PCM highway are allocated to the card (one time slot for respective circuit in the card) inserted in the slot number 0 of the shelf. Therefore, when all ten cards are fully mounted on the shelf, all time slots of the PCM highway are fully used.
However, when the card consisting six circuit is used, correspondence between time slot number of the PCM highway and mounting position of card becomes as shown in FIG. 5(b), i.e., the time slot number 1 to 6 are allocated to the card inserted in the slot number 0, and it is prohibited to use slot number 1, 3, 5, 7 and 9. FIG. 5(c) shows the case where the card is more integrated and one card consists of nine circuits. In this case, three cards of nine-circuit type and one card of three-circuit type are mounted on the shelf using slot numbers 0, 3, 6 and 9, and other slots are prohibited to use.
As described above, when some of cards, integrated a large number of circuits, are mounted on the shelf and all time slots of the PCM highway are used by them, other cards cannot be mounted in the remaining slots even if these slots are vacant.
To solve this problem, there is proposed a digital switching equipment with a system for extending a PCM highway.
The digital switching equipment of this type is, as disclosed in Japanese Unexamined Patent Application No. 5-64242, is characterized in that double PCM highways are connected to all card slots of a predetermined card slot group, respectively, and the selection of the double PCM highways is set by a selection setting switch.
FIG. 6 is a block diagram showing an example of the digital switching equipment of this type. The digital switching equipment has a time division switch 202 for switching time slots of PCM highways 201 and card slots 204 of card shelf are connected to the PCM highways 201. A card 203 consisting the plural number of line circuits or trunk circuits is inserted into the card slot for mounting on the card shelf. In the digital switching equipment, various types of timing signals are distributed from the time division switch 202 to all or a predetermined number of a plurality of card slot groups 205 each consisting of a plurality of card slots 204 by multiple-connection, and double PCM highways 201 are allotted to at least one of the plural card slot groups 205. The card, inserted into the card slot 204 of the card slot group 205 to which double PCM highways are allotted, is provided with a setting means of logical card slot position number. When all time slots of one PCM highway are used by other card in the card slot group, the card can set the logical card position number to select a time slot number to be used in other PCM highway and the card is inserted into a vacant card slot of the card slot group.
However, the digital switching equipment of this type has a problem that the capacity of the time division switch cannot be effectively utilized. Due to double PCM highways allocation to the same card slot, the extra PCM highway is allotted to the card slots which has used the first PCM highway. It means that there are time slots which cannot be actually used, and if the digital switching equipment is a large-scale switching equipment, there remains a number of time slots which are not effectively used and the time division switch becomes inappropriately larger in size, thereby causing a hike in costs.
It is an object of the present invention to realize a digital switching equipment provided with an extra PCM highway without an unnecessary increase in the capacity of the time division switch and without the need for the operation of the setting switch by operators.
A digital switching equipment provided with an extra PCM highway comprises a first PCM highway, which is connecting all card slots of a card shelf and a time division switch, and a second PCM highway, which is connecting predetermined card slots of the card shelf and a time division switch, for carrying digital information between line/trunk circuit and the time division switch, address setting means for providing one of first and second address information in each card slot of the card shelf, and selecting means, which is provided in each of line/trunk circuits, for selecting time slots of the first PCM highway when the first address information is provided, and selecting time slots of the second PCM highway when the second address information is provided.
Address setting means further comprises second address information setting means in the predetermined slot, to which the second PCM highway is connected, for outputting a second address information.
Line/trunk circuit according to the present invention comprises an address indicator for indicating second address information when the second address information is provided by the address setting means and for indicating first address information when the second address information is not provided by the address setting means, a highway selector for selecting and connecting a speech circuit of the line/trunk circuit to one of first and second PCM highways according to information indicated by the address indicator, and an address comparator for comparing address information on an address bus of a central control unit of the digital switching equipment to an address information provided by the address indicator, and for allowing the central control unit to access to a CPU of the line/trunk circuit when both address information are coincide with each other.
The address setting means comprises a address setting circuit which provides one of first and second address information in accordance with an instruction of a central control unit of the digital switching equipment.